U.S. patent number 8,275,594 [Application Number 11/927,281] was granted by the patent office on 2012-09-25 for engineered scaffolds for intervertebral disc repair and regeneration and for articulating joint repair and regeneration.
This patent grant is currently assigned to The Regents of the University of Michigan, Wisconsin Alumni Research Foundation. Invention is credited to James R. Adox, Stephen E. Feinberg, Scott J. Hollister, Frank LaMarca, Chia-Ying Lin, William L. Murphy.
United States Patent |
8,275,594 |
Lin , et al. |
September 25, 2012 |
Engineered scaffolds for intervertebral disc repair and
regeneration and for articulating joint repair and regeneration
Abstract
Methods for the engineering and preparation of intervertebral
disc repair scaffolds and articulating joint repair scaffolds are
disclosed. The methodology utilizes either magnetic resonance
images or combined magnetic resonance and computed tomography
images as a template for creating either the intervertebral
scaffold or the joint repair scaffold (e.g., osteochondral
scaffold) with fixation to the underlying bone. The disc scaffold
design may include an outer annulus that may contain desired
structures and a central nucleus pulposus region that could either
contain a designed microstructure or a contained hydrogel. The
osteochondral scaffold may include a bone compartment interface
with a cartilage compartment. The bone compartment may interface
with a cutout portion of the bone through fixation components.
Different microstructure designs may be created for the bone and
cartilage compartment to represent desired mechanical and mass
transport properties. The scaffolds are designed with a
microstructure that controls elastic and permeability property
distribution within the scaffold.
Inventors: |
Lin; Chia-Ying (Ann Arbor,
MI), LaMarca; Frank (Ann Arbor, MI), Feinberg; Stephen
E. (Ann Arbor, MI), Murphy; William L. (Madison, WI),
Adox; James R. (Ann Arbor, MI), Hollister; Scott J.
(Saline, MI) |
Assignee: |
The Regents of the University of
Michigan (Ann Arbor, MI)
Wisconsin Alumni Research Foundation (Madison, WI)
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Family
ID: |
39589163 |
Appl.
No.: |
11/927,281 |
Filed: |
October 29, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080195211 A1 |
Aug 14, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60855234 |
Oct 30, 2006 |
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Current U.S.
Class: |
703/11 |
Current CPC
Class: |
A61P
19/08 (20180101); A61F 2/389 (20130101); A61F
2/442 (20130101); A61F 2/30942 (20130101); A61F
2002/30761 (20130101); A61F 2002/30991 (20130101); A61F
2002/30948 (20130101); A61F 2250/0098 (20130101); A61F
2002/3097 (20130101); A61F 2002/30968 (20130101); A61F
2002/30593 (20130101); A61F 2310/00796 (20130101); A61F
2310/00976 (20130101); A61F 2002/30004 (20130101); A61F
2002/30032 (20130101); A61F 2002/30777 (20130101); A61F
2002/30841 (20130101); A61F 2250/0031 (20130101); A61F
2002/30616 (20130101); A61F 2230/0082 (20130101); A61F
2/3662 (20130101); A61F 2002/30062 (20130101); A61F
2002/30261 (20130101); A61F 2310/00293 (20130101); A61F
2002/30892 (20130101); A61F 2310/00023 (20130101); A61F
2210/0004 (20130101); B33Y 80/00 (20141201); A61F
2002/30789 (20130101); A61F 2250/0014 (20130101); A61F
2002/30014 (20130101); A61F 2002/30962 (20130101); A61F
2310/00017 (20130101); A61F 2002/2817 (20130101); A61F
2250/0063 (20130101); A61F 2/30767 (20130101); A61F
2002/3092 (20130101); A61F 2230/0069 (20130101); A61F
2002/30604 (20130101); A61F 2002/30785 (20130101); A61F
2002/3008 (20130101); A61F 2310/00029 (20130101); A61F
2/28 (20130101); A61F 2002/30224 (20130101); A61F
2002/30884 (20130101); A61F 2002/30578 (20130101); A61F
2002/30838 (20130101); A61F 2250/0018 (20130101); A61F
2002/30599 (20130101); A61F 2/2846 (20130101); B33Y
50/00 (20141201) |
Current International
Class: |
G06G
7/58 (20060101) |
Field of
Search: |
;703/11 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Sun et al., "Bio-CAD Modeling and Its Applications in
Computer-Aided Tissue Engineering," Computer-Aided Design (Sep. 15,
2005) vol. 37, pp. 1097-1114. cited by examiner.
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Primary Examiner: Lin; Jerry
Attorney, Agent or Firm: Quarles & Brady LLP
Government Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
This invention was made with government support under grant number
R01 DE 13608 and grant number AR 052893 awarded by the National
Institutes of Health. The government has certain rights in the
invention.
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority from U.S. Provisional Patent
Application No. 60/855,234 filed Oct. 30, 2006.
Claims
What is claimed is:
1. A method, implemented on a computer having at least a processor
and storage, for designing a tissue scaffold for generating tissue
in a patient, the method comprising: creating a first set of
databases representing a plurality of porous microstructure designs
for the scaffold in image based format; creating a second database
representing scaffold exterior geometry desired to replace the
native tissue in the patient in image based format; creating a
third database representing a plurality of scaffold external
fixation structures for attaching the scaffold to existing patient
tissue; and merging the first set of databases representing the
desired microstructure designs with the second database and the
third database into an image-based design of the scaffold.
2. The method of claim 1 further comprising: converting the
image-based design to a fabrication geometry.
3. The method of claim 1 wherein: the scaffold external fixation
structure is designed to comprise at least one projection extending
away from the scaffold.
4. The method of claim 3 wherein: the projection is a peg or a
spike or a plate.
5. The method of claim 1 wherein: the scaffold is designed for
intervertebral disc repair, or articulating joint repair, or total
joint replacement.
6. The method of claim 1 wherein the scaffold external fixation
structure for attaching the scaffold to existing patient tissue is
created using the first set of databases representing the plurality
of porous microstructure designs.
7. The method of claim 1 wherein the scaffold external fixation
structure for attaching the scaffold to existing patient tissue is
porous.
8. The method of claim 1 wherein the tissue is an intervertebral
disc.
9. A method implemented on a computer having at least a processor
and storage, for designing an intervertebral disc scaffold, the
method comprising: creating a first set of databases representing a
plurality of porous microstructure designs for the scaffold in
image based format including one or more regions designed to have
biochemical properties or to include bioactive agents; creating a
second database representing scaffold exterior geometry desired to
replace the native disc in the patient in image based format; and
merging the first set of databases representing the desired
microstructure designs with the second database into an image-based
design of the scaffold, and wherein the image-based design includes
a region designed to have a first biochemical property.
10. The method of claim 9 further comprising: converting the
image-based design to a fabrication geometry.
11. The method of claim 9 wherein: the image-based design of the
scaffold includes an outer annulus having a first designed porous
microstructure, and the image-based design of the scaffold includes
a central region having a second designed microstructure.
12. The method of claim 9 wherein: at least one of the
microstructure designs is a wavy fiber design.
13. The method of claim 9 wherein: the image-based design of the
scaffold is designed to include spherical or elliptical pores.
14. The method of claim 9 wherein the region designed to have a
first biochemical property comprises a polymer containing a
bioactive agent.
15. A method implemented on a computer having at least a processor
and storage, for designing an osteochondral scaffold for replacing
native tissue in a patient, the method comprising: creating a first
set of databases representing a plurality of porous microstructure
designs for the scaffold in image based format including one or
more regions designed to have biochemical properties or to include
bioactive agents; creating a second database representing scaffold
exterior geometry desired to replace the native tissue in the
patient in image based format; and merging the first set of
databases representing the desired microstructure designs with the
second database into an image-based design of the scaffold, wherein
the image-based design includes a bone region designed to have a
first biochemical property and a cartilage region designed to have
a second biochemical property.
16. The method of claim 15 wherein: the first biochemical property
is a mass transport property, and the second biochemical property
is a mass transport property.
17. The method of claim 15 wherein: the first biochemical property
is achieved by coating at least a portion of the bone region with
an osteoconductive mineral comprising a calcium compound.
18. The method of claim 15, wherein the bone region designed to
have a first biochemical property comprises a polymer containing a
bioactive agent.
19. A method implemented on a computer having at least a processor
and storage, for designing a joint replacement for a patient, the
method comprising: creating a first set of databases representing a
plurality of porous microstructure designs for the joint
replacement in image based format including one or more regions
designed to have biochemical properties or to include bioactive
agents; creating a second database representing joint replacement
exterior geometry in image based format; and merging the first set
of databases representing the desired microstructure designs with
the second database into an image-based design of the joint
replacement, wherein the image-based design includes a bone region
designed to have a first biochemical property and a surface region
designed to have a second biochemical property.
20. The method of claim 19 wherein: the first biochemical property
is a mass transport property, and the second biochemical property
is a mass transport property.
21. The method of claim 19 wherein: the first biochemical property
is achieved by coating at least a portion of the bone region with
an osteoconductive mineral comprising a calcium compound.
22. The method of claim 19 wherein the bone region designed to have
a first biochemical property comprises a polymer containing a
bioactive agent.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to biomaterial scaffolds, and more
particularly to biomaterial scaffolds for intervertebral disc
repair and/or regeneration and biomaterial scaffolds for
articulating joint repair and/or regeneration.
2. Description of the Related Art
It is reported in U.S. Patent Application Publication No.
2003/0069718 and corresponding U.S. Pat. No. 7,174,282 that
biomaterial scaffolds for tissue engineering perform three primary
functions. The first is to provide a temporary function (stiffness,
strength, diffusion, and permeability) in tissue defects. The
second is to provide a sufficient connected porosity to enhance
biofactor delivery, cell migration and regeneration of connected
tissue. The third requirement is to guide tissue regeneration into
an anatomic shape. It is further noted that the first two functions
present conflicting design requirements. Specifically, increasing
connected porosity to enhance cell migration and tissue
regeneration decreases mechanical stiffness and strength, whereas
decreasing porosity increases mechanical stiffness and strength but
impedes cell migration and tissue regeneration.
U.S. 2003/0069718 provides a design methodology for creating
biomaterial scaffolds with internal porous architectures that meet
the need for mechanical stiffness and strength and the need for
connected porosity for cell migration and tissue regeneration. The
design methods of U.S. 2003/0069718 combine image-based design of
pore structures with homogenization theory to compute effective
physical property dependence on material microstructure.
Optimization techniques are then used to compute the optimal pore
geometry. The final optimized scaffold geometry voxel topology is
then combined with a voxel data set describing the three
dimensional anatomic scaffold shape which may be obtained by
magnetic resonance (MR) images or combined MR and computed
tomography (CT) images. Density variations within the anatomic
scaffold voxel database are used as a map to guide where different
optimized scaffold voxel topologies are substituted. The final
voxel representation of the anatomically shaped scaffold with
optimized interior architecture is then converted automatically by
software into either a surface representation or wire frame
representation for fabrication of the scaffold by way of solid free
form fabrication or casting.
While the advances of U.S. 2003/0069718 have significantly improved
the design of biomaterial scaffolds for tissue engineering, there
is still a need for further advances in this technology to provide
for even more optimized biomaterial scaffolding and tissue
generation systems.
SUMMARY OF THE INVENTION
The present invention provides methods for the engineering and
preparation of scaffolding and tissue generation systems for the
repair of bone/cartilage composites, including, but not limited to,
osteochondral scaffolds/tissue repair systems for the tibial
plateau, proximal femoral head, acetabulum, humeral head, and
intervertebral spinal disc repair and regeneration. The methodology
utilizes either magnetic resonance images or combined magnetic
resonance and computed tomography images as a template for creating
either the intervertebral scaffold as well as the fixation for the
scaffolding into adjacent vertebral bodies or the osteochondral
scaffold with fixation to the underlying bone.
The disc scaffold design may include an outer annulus that may
contain desired porous structures and a central nucleus pulposus
region that could either contain a designed porous microstructure
or a contained hydrogel or other bioactive agent(s).
Instrumentation for surgical placement is also included. The
scaffolding has designed microstructure that controls elastic and
permeability property distribution within the intervertebral
zone.
The osteochondral scaffold may include a bone compartment interface
with a cartilage compartment. The bone compartment may interface
with a cutout portion of the bone through fixation components such
as pegs and screws and the like. Different microstructure designs
may be created for the bone and cartilage compartment to represent
desired mechanical and mass transport properties.
Advantages of the method of the invention include the ability to
create designed microstructures that can mimic intervertebral load
carrying capability, to provide directed nutrients to
seeded/migrated cells in the disc, and the capability of creating
disc structures that can regrow natural tissue. This provides a
potential advantage over artificial discs, which as synthetic
materials are subject to wear and fatigue failure. Regrowth of a
new disc would provide a natural tissue that could remodel in
response to applied loads and would be subject to the wear and
fatigue problems of synthetic materials. In addition, the
capability of creating designed scaffolding would provide the
necessary load bearing capability via designed elasticity and
permeability for tissue engineering an intervertebral disc that
non-designed scaffolds could not provide. In addition, if the
designed scaffolding is used for fusion, it could provide load
bearing capability that would eliminate the need for some or all of
the hardware needed for current interbody fusion techniques.
For the osteochondral scaffold, advantages include the ability to
design a separate bone/cartilage interface, and more importantly,
the ability to design these bone and cartilage compartments to have
desired effective mechanical and mass transport properties. In
addition, the osteochondral scaffolds could have virtually any
interface with surrounding tissue or for surgical fixation.
For the total joint interface, advantages again include the ability
to have control over the designed microstructure interface, giving
it desired interface elasticity properties and the ability to
control geometric thickness.
In one aspect of the invention, there is provided a method for
designing a tissue scaffold for generating tissue in a patient. In
the method, a first set of databases is created representing a
plurality of porous microstructure designs for the scaffold in
image based format. A second database is created representing
scaffold exterior geometry desired to replace the native tissue in
the patient in image based format. A third database is created
representing scaffold external fixation structure. Then, the first
set of databases representing the desired microstructure designs
and the second database and the third database are merged into an
image-based design of the scaffold. The image-based design may then
be converted to a fabrication geometry such as surface
representation or wireframe representation.
In one form, the scaffold external fixation structure is designed
to be porous, and is designed to include at least one projection
extending away from the scaffold. Example projections are a peg or
a spike or a plate. The projection can be designed to include
fastening means selected from threads and/or throughholes. In one
embodiment, the scaffold is designed for intervertebral disc
repair. In another embodiment, the scaffold is designed for
articulating joint repair. In yet another embodiment, the scaffold
is designed for total joint replacement.
The scaffold external fixation structure can be designed to include
at least one projection extending away from the scaffold, and at
least one marking including a tracer that provides enhanced
visibility via a medical imaging device can be placed on the at
least one projection. The scaffold external fixation structure can
be designed to include at least one projection extending away from
the scaffold, and at least one radiopaque marking that provides
enhanced visibility via a fluoroscope can be placed on the at least
one projection. The scaffold can be designed to include a region of
no material or radiolucent material such that the region forms an
imaging window for enhanced visibility through the imaging window
via a medical imaging device. The scaffold external fixation
structure can be designed to include at least one projection
extending away from the scaffold, and at least one marking for
alignment during implantation can be placed on the at least one
projection.
In another aspect of the invention, there is provided a method for
designing an intervertebral disc scaffold. In the method, a first
set of databases is created representing a plurality of porous
microstructure designs for the scaffold in image based format. A
second database is created representing scaffold exterior geometry
desired to replace the native disc in the patient in image based
format. Then, the first set of databases representing the desired
microstructure designs are merged with the second database into an
image-based design of the scaffold. The image-based design can be
converted to a fabrication geometry. The second database can
represent an intervertebral space to be occupied by the
scaffold.
In one form, the image-based design of the scaffold can be designed
to include an outer annulus having a first designed porous
microstructure, and the image-based design of the scaffold can be
designed to include a central region having a second designed
microstructure. In another form, the image-based design of the
scaffold can be designed to include an outer annulus having a first
designed porous microstructure, and the image-based design of the
scaffold can be designed to include a central region designed for
containing a biocompatible material. At least one of the
microstructure designs can be a wavy fiber design. In one form, the
image-based design of the scaffold is designed to include spherical
or elliptical pores.
The scaffold can be designed to include at least one projection,
such as a plate, peg or spike, extending away from the scaffold,
and at least one marking including a tracer that provides enhanced
visibility via a medical imaging device can be placed on the at
least one projection. The scaffold can be designed to include at
least one projection extending away from the scaffold, and at least
one radiopaque marking that provides enhanced visibility via a
fluoroscope can be placed on the at least one projection. The
scaffold can be designed to include at least one projection
extending away from the scaffold, and at least one marking for
alignment during implantation can be placed on the at least one
projection. The scaffold can be designed to include a region of no
material or radiolucent material such that the region forms an
imaging window for enhanced visibility through the imaging window
via a medical imaging device.
In yet another aspect of the invention, there is provided a method
for designing an osteochondral scaffold for replacing native tissue
in a patient. In the method, a first set of databases is created
representing a plurality of porous microstructure designs for the
scaffold in image based format. A second database is created
representing scaffold exterior geometry desired to replace the
native tissue in the patient in image based format. The first set
of databases representing the desired microstructure designs are
merged with the second database into an image-based design of the
scaffold that includes a bone region designed to have a first
physical or biochemical property and a cartilage region designed to
have a second physical or biochemical property. At least one of the
microstructure designs can be a wavy fiber design. The bone region
can be designed to have a pore structure different from a pore
structure of the cartilage region. The cartilage region can be
designed to include spherical or elliptical pores. The bone region
can be designed to allow greater mass transport than the cartilage
region.
The first physical or biochemical property can be a mechanical
property (such as elasticity), and the second physical or
biochemical property can be a mechanical property (such as
elasticity). The first physical or biochemical property can be a
mass transport property (such as permeability), and the second
physical or biochemical property can be a mass transport property
(such as permeability). The first physical or biochemical property
can be a biochemical property (such as bioactive agent delivery
control), and the second physical or biochemical property can be a
biochemical property (such as bioactive agent delivery
control).
In one embodiment, the first physical or biochemical property can
be achieved by coating at least a portion of the bone region with
an osteoconductive mineral. In another embodiment, the first
physical or biochemical property can be achieved by coating at
least a portion of the bone region with an osteoconductive mineral
comprising a calcium compound. In yet another embodiment, the first
physical or biochemical property can be achieved by coating at
least a portion of the bone region with an osteoconductive mineral
comprising a material selected from hydroxyapatite,
calcium-deficient carbonate-containing hydroxyapatite, tricalcium
phosphate, octacalcium phosphate, dicalcium phosphate, calcium
phosphate, and mixtures thereof. In still another embodiment, the
first physical or biochemical property can be achieved by coating
at least a portion of the bone region with an osteoconductive
mineral comprising a plurality of discrete mineral islands. In yet
another embodiment, the first physical or biochemical property can
be achieved by coating at least a portion of the bone region with
an osteoconductive mineral comprising a substantially homogeneous
mineral coating. In still another embodiment, the first physical or
biochemical property can be achieved by coating at least a portion
of the bone region with an osteoconductive mineral and associating
a bioactive agent with the mineral coating. The bioactive agent can
be selected from bone morphogenetic proteins.
In yet another aspect of the invention, there is provided a method
for designing a joint replacement for a patient. In the method, a
first set of databases is created representing a plurality of
porous microstructure designs for the joint replacement in image
based format. A second database is created representing joint
replacement exterior geometry in image based format. The first set
of databases representing the desired microstructure designs are
merged with the second database into an image-based design of the
joint replacement that includes a bone region designed to have a
first physical or biochemical property and a surface region
designed to have a second physical or biochemical property. At
least one of the microstructure designs can be a wavy fiber design.
The bone region can be designed to have a pore structure different
from a pore structure of the surface region. The surface region can
be designed to include spherical or elliptical pores. The bone
region can be designed to allow greater mass transport than the
cartilage region.
The first physical or biochemical property can be a mechanical
property (such as elasticity), and the second physical or
biochemical property can be a mechanical property (such as
elasticity). The first physical or biochemical property can be a
mass transport property (such as permeability), and the second
physical or biochemical property can be a mass transport property
(such as permeability). The first physical or biochemical property
can be a biochemical property (such as bioactive agent delivery
control), and the second physical or biochemical property can be a
biochemical property (such as bioactive agent delivery
control).
In one embodiment, the first physical or biochemical property can
be achieved by coating at least a portion of the bone region with
an osteoconductive mineral. In another embodiment, the first
physical or biochemical property can be achieved by coating at
least a portion of the bone region with an osteoconductive mineral
comprising a calcium compound. In yet another embodiment, the first
physical or biochemical property can be achieved by coating at
least a portion of the bone region with an osteoconductive mineral
comprising a material selected from hydroxyapatite,
calcium-deficient carbonate-containing hydroxyapatite, tricalcium
phosphate, octacalcium phosphate, dicalcium phosphate, calcium
phosphate, and mixtures thereof. In still another embodiment, the
first physical or biochemical property can be achieved by coating
at least a portion of the bone region with an osteoconductive
mineral comprising a plurality of discrete mineral islands. In yet
another embodiment, the first physical or biochemical property can
be achieved by coating at least a portion of the bone region with
an osteoconductive mineral comprising a substantially homogeneous
mineral coating. In still another embodiment, the first physical or
biochemical property can be achieved by coating at least a portion
of the bone region with an osteoconductive mineral and associating
a bioactive agent with the mineral coating. The bioactive agent can
be selected from bone morphogenetic proteins.
In still another aspect of the invention, there is provided an
intervertebral disc repair and/or regeneration scaffold. The
scaffold includes a central core shaped to approximate the nucleus
pulposus of a natural intervertebral disc wherein the central core
has a first porous microstructure. The scaffold further includes an
outer annulus shaped to approximate the annulus fibrosus of a
natural intervertebral disc wherein the outer annulus is connected
to and surrounds the central core and wherein the outer annulus has
a second porous microstructure. In one embodiment, the central core
and the outer annulus have different elasticity. In another
embodiment, the central core and the outer annulus have different
permeability. In yet another embodiment, the central core and the
outer annulus have different bioactive agent release
properties.
In one form, the central core includes a biocompatible material. In
another form, the central core includes a hydrogel. In yet another
form, the central core includes a bioactive agent. In one
embodiment, the bioactive agent is selected from undifferentiated
chondrocyte precursor cells from periosteum, mesenchymal stem cells
from bone marrow, chondrocytes, sclerosing agents, angiogenesis
activators, angiogenesis inhibitors, and mixtures thereof. The
central core can comprise wavy fibers.
The scaffold can be formed from biodegradable polymers,
biodegradable ceramics, non-biodegradable metals, non-biodegradable
metal alloys, or mixtures thereof. The scaffold can include at
least one marking including a tracer that provides enhanced
visibility via a medical imaging device. The scaffold can include
at least one radiopaque marking that provides enhanced visibility
via a fluoroscope. The scaffold can include a region of no material
or radiolucent material such that the region forms an imaging
window for enhanced visibility through the imaging window via a
medical imaging device. The scaffold can include at least one
marking for alignment during implantation.
In one embodiment, an osteoconductive mineral coating is disposed
on at least a portion of the scaffold. The osteoconductive mineral
coating can include a plurality of discrete mineral islands.
Alternatively, the osteoconductive mineral coating can include a
substantially homogeneous mineral coating. The osteoconductive
mineral coating can include a calcium compound. For example, the
osteoconductive mineral coating can include hydroxyapatite,
calcium-deficient carbonate-containing hydroxyapatite, tricalcium
phosphate, octacalcium phosphate, dicalcium phosphate, calcium
phosphate, and mixtures thereof. A bioactive agent can be
associated with the mineral coating. Example bioactive agent are
bone morphogenetic proteins.
These and other features, aspects, and advantages of the present
invention will become better understood upon consideration of the
following detailed description, drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a slice from an external shape design dataset for an
intervertebral disc. The internal rings represent the different
density regions for mapping heterogeneous microstructure.
FIG. 2A shows an example of a designed microstructure for
scaffolding with interconnected cylindrical pores.
FIG. 2B shows an example of a designed microstructure for
scaffolding with topology optimized microstructure.
FIG. 2C shows an example of a designed microstructure for
scaffolding with wavy fibered microstructure.
FIG. 3 shows a slice of a designed intervertebral scaffolding with
wavy fibered microstructure in the correct anatomic shape. The
central region approximates the shape of the nucleus pulposus in a
natural intervertebral disc.
FIG. 4 shows an example of an integrated anterior plate fixation on
a disc regeneration scaffold. This integrated plating can be used
for either disc regeneration or spinal fusion.
FIG. 5A shows an example of a spiked vertebrae interface on the top
of an intervertebral disc scaffold.
FIG. 5B shows an example of a spiked vertebrae interface on the
bottom of the intervertebral disc scaffold of FIG. 5A.
FIG. 6 shows a density map for a tibial plateau.
FIG. 7 shows an example final osteochondral scaffold with desired
shape and microstructure.
FIG. 8 shows the fit of a designed osteochondral scaffold into the
whole tibia.
FIG. 9 shows a stem simulating a hip stem with a designed
microstructure as an interface for fixation of the stem to
surrounding bone.
FIG. 10 shows the steps in engineering a mandibular condyle
scaffold from image to fabricated scaffold.
FIG. 11 shows an example of a cervical disc regeneration scaffold
with designed anterior fixation plate and wavy fiber microstructure
fabricated from polycaprolactone (PCL).
Like reference numerals will be used to refer to like or similar
parts from Figure to Figure in the following description.
DETAILED DESCRIPTION OF THE INVENTION
An intervertebral disc scaffolding according to the invention
includes: (i) a designed porous microstructured scaffolding itself,
made from biodegradable polymers (e.g., polycaprolactone),
biodegradable ceramics (e.g., calcium phosphate), or
non-biodegradable metals or metal alloys (e.g., titanium or
titanium alloys), or mixtures thereof, and (ii) fixation structures
for integrating the designed intervertebral scaffolding to the
adjacent vertebrae. As used herein, a "biodegradable" material is
one which decomposes under normal in vivo physiological conditions
into components which can be metabolized or excreted.
The scaffolding may include a bioactive agent at any desired
location in the scaffold. A "bioactive agent" as used herein
includes, without limitation, physiologically or pharmacologically
active substances that act locally or systemically in the body. A
bioactive agent is a substance used for the treatment, prevention,
diagnosis, cure or mitigation of disease or illness, or a substance
which affects the structure or function of the body or which
becomes biologically active or more active after it has been placed
in a predetermined physiological environment. Bioactive agents
include, without limitation, cells, enzymes, organic catalysts,
ribozymes, organometallics, proteins (e.g., bone morphogenetic
proteins), demineralized bone matrix, bone marrow aspirate,
undifferentiated chondrocyte precursor cells from periosteum,
mesenchymal stem cells from bone marrow, chondrocytes, sclerosing
agents, angiogenesis activators, angiogenesis inhibitors,
glycoproteins, peptides, polyamino acids, antibodies, nucleic
acids, steroidal molecules, antibiotics, antimycotics, cytokines,
fibrin, collagen, fibronectin, vitronectin, hyaluronic acid, growth
factors (e.g., transforming growth factors and fibroblast growth
factor), carbohydrates, statins, oleophobics, lipids, extracellular
matrix and/or its individual components, pharmaceuticals, and
therapeutics.
In areas of the scaffold where bone growth is desired, preferred
bioactive agents include, without limitation, bone morphogenetic
proteins (such as rhBMP-2, BMP-2, BMP-4, BMP-7, BMP-14),
demineralized bone matrix, bone marrow aspirate, growth and
development factor-5 (GDF-5), or platelet rich plasma (PRP). In
areas of the scaffold where cartilage or fibrous tissue growth is
desired, preferred bioactive agents include, without limitation,
undifferentiated chondrocyte precursor cells from periosteum,
mesenchymal stem cells from bone marrow, chondrocytes, sclerosing
agents (such as surfactants, polidocanol, and sodium morrhuate),
angiogenesis activators, and angiogenesis inhibitors.
The starting point for creating the scaffold may be either a CT
image MR image, a combined MR/CT image, or a digitized cadaver
vertebral image. The resulting images provide the external shape
and design space for the disc scaffolding and fixation. These
images are stored as density distribution within a voxel dataset.
In addition, the tissue density distribution from the images
provides a flag for placing the designed microstructure within the
global design space. In addition, the global density distribution
used as a mapping flag may also be created using global topology
optimization. An example of a global density distribution of a
cross-sectional intervertebral disc image 20 is shown in FIG. 1
wherein the internal rings mark the different density regions for
mapping heterogeneous microstructure.
A porous microstructure design may be created using the image based
design methods described in U.S. Patent Application Publication No.
2003/0069718, which is incorporated herein by reference as if fully
set forth herein. The steps for performing the scaffold
optimization of the present invention using the image based design
methods described in U.S. Patent Application Publication No.
2003/0069718 are as follows. In step 1, the methodology creates
unit cell voxel databases. That is, a set of base unit cell
architectures are created in voxel format ranging over all design
parameters. In step 2, the method calculates effective physical
properties. That is, the method solves homogenization equations for
each unit cell to calculate effective physical property of the
scaffold and the tissue that will grow into the scaffold pores. The
method can also determine functional dependence of effective
stiffness, permeability, and porosity on cell design parameters. In
step 3, the method formulates and solves optimization algorithms of
unit cell parameters. That is, the method solves the optimization
problem that will find the best match of both scaffold and
regenerate tissue properties to naturally occurring tissue
properties. The solution gives the optimal design parameters for
the unit cell architecture. In step 4, the method creates an
anatomic shape voxel database. That is, the method creates a voxel
database of the anatomic scaffold shape with different densities
representing different scaffold architectures. In step 5, the
method merges the anatomic and unit cell architecture data base.
That is, the method uses image-based Boolean operations to merge
the anatomic data base with density distribution with individual
sets of unit cell databases. In step 6, the method converts the
voxel design to a surface or wire frame geometry. That is, the
method converts the resulting complete scaffold design in voxel
format to either a triangular facet representation or a wire frame
representation that can be used in solid free form systems. In step
7, the method fabricates the design scaffold from biomaterial using
direct or indirect (casting) solid free form techniques.
In the present invention, the scaffold microstructure will be
created to provide a specified heterogeneous distribution of
effective elastic and permeability properties, designed to provide
load bearing capability similar to a natural human intervertebral
disc, along with pathways for nutrient nutrition. The
microstructure design may comprise, but is not limited to, the
following: (1) an interconnected system of spherical pores with
varying diameter; (2) an interconnected system of straight or
curved struts with varying diameter; (3) topology optimized
microstructures; or (4) wavy fibered structures. FIG. 2A shows an
example of a designed microstructure 22 for scaffolding with
interconnected cylindrical pores. FIG. 2B shows an example of a
designed microstructure 24 for scaffolding with topology optimized
microstructure. FIG. 2C shows an example of a designed
microstructure 26 for scaffolding with wavy fibered
microstructure.
In the microstructure design, the image-based methods as in U.S.
2003/0069718 can be used to design an internal architecture
optimized to match target bone or cartilage Young's moduli. In
particular, the modulus ranges for trabecular bone and
intervertebral disc that we would target for fusion and disc repair
are: Bone: 30-200 MPa, and Intervertebral Disc: 0.4-10 MPa.
This microstructure may be created by repeating basic unit cell
design blocks. These unit cell blocks are also represented as a
density distribution within a structured voxel dataset. Once the
unit cell designs and global shape template image databases are
created, they are merged using image Boolean operations to create
the final design porous microstructure scaffolding as described in
U.S. Patent Application Publication No. 2003/0069718. A prototype
for a designed intervertebral disc repair and/or regeneration
scaffolding is shown in FIG. 3. FIG. 3 shows a cross section of a
designed intervertebral scaffolding 30 with wavy fibered
microstructure 32 in the correct anatomic shape. The central region
34 approximates the shape of the nucleus pulposus in a natural
intervertebral disc. The outer region 36 approximates the shape of
the outer annulus fibrosus in a natural intervertebral disc.
The next step in creating the scaffolding is to create a fixation
structure for attaching the disk scaffolding to the adjacent
vertebrae. This fixation structure is also created using the same
combination of microstructure and global design datasets, as it may
be porous to allow bone ingrowth. This fixation may take many
forms. One example fixation is a plate attached directly to the
scaffold disc. An example of this fixation is shown in the scaffold
40 of FIG. 4.
In FIG. 4, the wavy fibered microstructure 32 is in the correct
anatomic shape for a natural intervertebral disc. A top fixation
plate 45 includes spaced apart fastener holes 46a, 46b and a top
central U-shaped cutaway section 47. A bottom fixation plate 51
includes spaced apart fastener holes 52a, 52b, and a bottom central
inverted U-shaped cutaway section 53. The wavy fibered
microstructure 32 is integral with the fixation plates 45, 51. When
used in intervertebral disc repair, the wavy fibered microstructure
32 of the scaffold 40 would be positioned in the intervertebral
space created by removal of the intervertebral disc between
adjacent vertebrae. Fasteners would be inserted in fastener holes
46a, 46b for anterior attachment to a first upper vertebra, and
fasteners would be inserted in fastener holes 52a, 52b for anterior
attachment to an adjacent second lower vertebra. The top end
surface 54 of the wavy fibered microstructure 32 would contact a
lower surface of the first upper vertebra, and the opposite bottom
end surface 55 of the wavy fibered microstructure 32 would contact
an upper surface of the second lower vertebra. The wavy fibered
microstructure 32 thereby provides mechanical load bearing support
between the first upper vertebra and the second lower vertebra.
The vertical dimensions of the wavy fibered microstructure 32 can
be adjusted accordingly for various different intervertebral
distances. Likewise, the horizontal length of the fixation plates
45, 51 and their spatial relationship can be varied to ensure
proper location of the fastener holes 46a, 46b, 52a, 52b adjacent
the first upper vertebra and the second lower vertebra for securing
the scaffold 40 to the first upper vertebra and the second lower
vertebra. By varying the dimensions of the wavy fibered
microstructure 32 and the fixation plates 45, 51, different size
scaffolds 40 can be provided for selection by a surgeon.
The scaffold 40 can comprise a porous biocompatible and
biodegradable (if desired) porous material selected from polymeric
materials, metallic materials, ceramic materials and mixtures
thereof. In one example embodiment, the scaffold 40 is formed from
polycaprolactone, a biocompatible and biodegradable polymer.
However, other polymers such as polylactide, polyglycolide,
poly(lactide-glycolide), poly(propylene fumarate),
poly(caprolactone fumarate), polyethylene glycol, and
poly(glycolide-co-caprolactone) may be advantageous for forming the
scaffold 40. As used herein, a "biocompatible" material is one
which stimulates only a mild, often transient, implantation
response, as opposed to a severe or escalating response.
An osteoconductive mineral coating can formed on at least a portion
of the scaffold 40 where bone growth is desired. The
osteoconductive mineral coating can comprises a plurality of
discrete mineral islands, or the mineral coating can be formed on
the entire surface areas of the scaffold 40. In one example form,
the osteoconductive mineral coating comprises a substantially
homogeneous mineral coating. In one example embodiment, the mineral
coatings may be any suitable coating material containing calcium
and phosphate, such as hydroxyapatite, calcium-deficient
carbonate-containing hydroxyapatite, tricalcium phosphate,
amorphous calcium phosphate, octacalcium phosphate, dicalcium
phosphate, calcium phosphate, and the like. The mineral coating may
also include a plurality of layers having distinct dissolution
profiles to control dissolution order, kinetics and bioactive
delivery properties. Under physiological conditions, the solubility
of calcium phosphate materials are as follows: amorphous calcium
phosphate>dicalcium phosphate>octacalcium
phosphate>tricalcium phosphate>hydroxyapatite. Thus, a
plurality of various calcium phosphate layers can provide a broad
range of dissolution patterns. Incorporation of blank layers (i.e.,
calcium phosphate layers not containing any bioactive agent) can
provide for delayed release. Also, the incorporation of layers
having different concentrations of bioactive agent can provide for
varying release rates.
A bioactive agent can be associated with uncoated biocompatible
material forming the scaffold 40 and/or the mineral coated portions
of the scaffold 40. Different release rates of the bioactive agent
would be possible from uncoated and coated areas of the scaffold
40. While various bioactive agents listed above are suitable for
use with the scaffold 40, in one example embodiment, the bioactive
agent is selected from bone morphogenetic proteins, demineralized
bone matrix, bone marrow aspirate, and mixtures thereof. Bone
morphogenetic proteins have been shown to be excellent at growing
bone and powdered recombinant human BMP-2 is available in certain
commercial products. Demineralized bone matrix includes
osteoinductive proteins (e.g., bone morphogenetic proteins), and
can be used in a particle or fiber form. Bone marrow aspirate
contains osteoprogenitor cells, and the patient's bone marrow can
be readily harvested with a needle. As used herein, a bioactive
agent is "associated" with the polymer and/or the coating if the
bioactive agent is directly or indirectly, physically or chemically
bound to the polymer and/or the coating. A bioactive agent may be
physically bound to the polymer and/or the coating by entrapping,
imbedding or otherwise containing a bioactive agent within the
polymer and/or the coating network structure. A bioactive agent may
be chemically bound to the polymer and/or the coating by way of a
chemical reaction wherein a bioactive agent is covalently or
ionically bonded to the polymer and/or the coating. Thus, various
techniques for associating a bioactive agent in or on the polymer
and/or the coating are contemplated herein.
The bioactive agent is present in amount that induces ossification
or fibrous tissue growth depending on the effect desired. The
amount of bioactive agent included on uncoated and/or coated areas
of the scaffold 40 will depend on a variety of factors including
the nature of the bioactive agent, the osteoinductive potential of
the bioactive agent, and the nature of the carrier material (e.g.,
the biocompatible material forming the scaffold 40 or the mineral
coating on the scaffold 40). Investigations have shown that a 1-100
ng/ml concentration of BMP can induce osteogenesis; and in one
example, the BMP in the present invention can be released from the
scaffold 40 in a time frame that varies from 10-50 days. Therefore,
without intending to limit the invention in any way, in the case of
bone morphogenetic proteins, it is contemplated that in one example
a concentration of about 10-5000 ng of bone morphogenetic protein
per cm.sup.3 of material would be suitable for inducing
ossification between the adjacent bones or adjacent bone
surfaces.
Various regions of the scaffold 40 can include the coatings and
associated bioactive agent. For example, the plates 45, 51 that are
secured to the opposed vertebrae can be coated with continuous
coating or islands of the coating and a bioactive agent associated
with the coating so that bone growth is induced, while interior
sections of the scaffold may not include coatings and may include
different associated bioactive agents in order to promote growth of
fibrous tissue. As an exemplary illustration, plates 45, 51 in FIG.
4 could include a continuous mineral coating and associated
bioactive agent so that bone fixation to the adjacent vertebra is
induced, while the wavy fibered microstructure 32 may include
undifferentiated chondrocyte precursor cells from periosteum,
mesenchymal stem cells from bone marrow, chondrocytes, sclerosing
agents, angiogenesis activators, and/or angiogenesis inhibitors so
fibrous growth is promoted in this region.
Preferably, the bioactive agents (e.g., bone morphogenetic
proteins, chondrocytes) are associated with uncoated biocompatible
material forming the scaffold 40 and/or the mineral coated portions
of the scaffold 40 prior to inserting the wavy fibered
microstructure 32 in the intervertebral disc space. For example, a
bone morphogenetic protein may be chemically bonded (e.g.,
ionically or covalently bonded) to a calcium phosphate coating at a
manufacturing site, or alternatively a bone morphogenetic protein
may be chemically bonded to the calcium phosphate coating by a
surgeon before and/or after implantation. The surgeon can
reconstitute powdered bone morphogenetic protein with sterile water
and apply the reconstituted powdered bone morphogenetic protein to
the scaffold 40. Likewise, chondrocytes could be bonded to the wavy
fibered microstructure 32 by a surgeon, or at the manufacturing
site.
Alternatively, fixation to the first upper vertebra and the
adjacent second lower vertebra can be created as a keel riser
structure, as shown in FIGS. 5A and 5B. The scaffold 60 of FIGS. 5A
and 5B includes a wavy fibered microstructure 32a having top
projections 61 from a top surface 62 of the scaffold 60 and bottom
projections 63 from a bottom surface of the scaffold 60. When used
in intervertebral disc repair, the wavy fibered microstructure 32a
of the scaffold 60 would be positioned in the intervertebral space
created by removal of the intervertebral disc between adjacent
vertebrae. The top projections 61 would assist attachment to a
bottom surface of the first upper vertebra, and the bottom
projections 63 would assist attachment to the top surface an
adjacent second lower vertebra.
The fixation structures, the attached plate structure and/or keel
structure, will be porous polymers, ceramics and metals that may be
made as composites with the actual disk scaffolding. The final
scaffolding structure will be created by Boolean intersection of
the fixation structures image design database with the scaffolding
structure image design database. The final result will be a
designed, porous scaffolding structure that forms a composite with
the designed, porous fixation structures, as shown in FIG. 4 or
FIGS. 5A and 5B.
For the osteochondral scaffolding, the same fixation design
procedure is used. FIG. 6 shows a density map 70 for the tibial
plateau where lines 71, 72 mark the different density regions for
mapping heterogeneous microstructure. In this case, microstructures
similar to those designs in FIGS. 2A, 2B and 2C, including but not
limited to the wavy fiber design 32 may be used to create
functionally graded structures for the osteochondral scaffold.
These designs are then substituted into density map 70 of FIG. 6 to
create a scaffold design with desired shape and microstructure,
along with fixation pegs. FIG. 7 shows an example final
osteochondral scaffold 80 with desired shape and microstructure.
The scaffold 80 includes a tibial plateau 82 having fixation pegs
83 extending downward from a bottom surface 84 of the scaffold 80.
Preferably, the tibial plateau 82 region is designed to include
spherical or elliptical pores in order to enhance cartilage growth.
Also, the tibial plateau 82 region may be designed to have a lower
elasticity than the pegs 83 to promote cartilage growth. The final
fit of the osteochondral scaffold 80 in the tibial plateau 85 of a
tibia 86 is shown in FIG. 8.
The scaffold 80 can comprise a porous biocompatible and
biodegradable (if desired) porous material selected from polymeric
materials, metallic materials, ceramic materials and mixtures
thereof. In one example embodiment, the scaffold 80 is formed from
polycaprolactone, a biocompatible and biodegradable polymer.
However, other polymers such as polylactide, polyglycolide,
poly(lactide-glycolide), poly(propylene fumarate),
poly(caprolactone fumarate), polyethylene glycol, and
poly(glycolide-co-caprolactone) may be advantageous for forming the
scaffold 80.
An osteoconductive mineral coating can formed on at least a portion
of the scaffold 80 where bone growth is desired. Bioactive agents
would also be beneficial in the scaffold 80 of FIG. 7. For example,
a bone morphogenetic protein may be chemically bonded (e.g.,
ionically or covalently bonded) to a calcium phosphate coating at
the bottom surface 84 of the scaffold 80 for fixation to the tibia
86, while chondrocytes could be bonded to the tibial plateau 82 for
cartilage growth.
In addition to being used for porous osteochondral scaffolds, the
current designed microstructures could be used as bone interfaces
for more traditional total joint replacements. In this case, a
porous microstructure designed to have desired mechanical and mass
transport properties would be designed to cover a joint replacement
surface. The joint structure could be scanned using CT methods and
the designed microstructure would be combined using Boolean
methods. FIG. 9 shows such a combination for a simple solid stem 90
with a designed coating microstructure 92. The stem simulates a hip
stem with a designed microstructure as an interface for fixation of
the stem to surrounding bone.
If it is desired to create a scaffolding to engineer a new
intervertebral disc, then the fabrication materials may include a
composite of a degradable polymer for the structural scaffolding
and a hydrogel interspersed within the designed scaffolding. A
bioactive agent may also be included in the scaffolding. The
degradable polymer may include one of the following, but is not
limited to: (1) Polycaprolactone; (2) Polylactic Acid; (3)
Polylactic-Polyglycolic Acid Co-polymer; (4) Polypropylene
Fumarate; (5) Poly(glycerol-sebacate), and (6) Poly Octane Diol
Citrate. The hydrogel may include, but is not limited to: (1)
Fibrin Gel; (2) Polyethylene Glycol (PEG); (3) Collagen I Gel; and
(4) Collagen/Hyaluronic Acid Gel.
If it is desired to create an intervertebral fusion device, then
the scaffolding material may, in addition to the degradable
polymers listed above, may also include, but is not limited to, the
following: (1) Calcium Phosphate Ceramic; (2) Calcium Phosphate
Ceramic/Polymer Composite; and (3) Titanium.
For an osteochondral scaffold, similar materials may be used to
engineer the cartilage component including: (1) Polycaprolactone;
(2) Polylactic Acid; (3) Polylactic-Polyglycolic Acid Co-polymer;
(4) Polypropylene Fumarate, (5) poly(glycerol-sebacate), and (6)
Poly Octane Diol Citrate. The hydrogel may include, but is not
limited to: (1) Fibrin Gel; (2) Polyethylene Glycol (PEG); (3)
Collagen I Gel; and (4) Collagen/Hyaluronic Acid Gel.
For the bone portion of the osteochondral scaffold, the materials
may include polymer, ceramics or metals. Polymers may include, but
are not limited to: (1) Polycaprolactone; (2) Polylactic Acid; (3)
Polylactic-Polyglycolic Acid Co-polymer; and (4) Polypropylene
Fumarate. These polymers may be surface engineered to include a
biomineralized surface layer to improve osteoconductivity using a
technique such as that described in U.S. Pat. No. 6,767,928, which
is incorporated herein by reference as if fully set forth herein.
In addition, both ceramics and metals may be used to fabricate the
bone portion, including but not limited to: (1) Calcium Phosphate
Ceramic; (2) Calcium Phosphate Ceramic/Polymer Composite; and (3)
Titanium. The osteochondral scaffold may also include a bioactive
agent in the bone and/or cartilage portion.
For the total joint replacement with a designed microstructure
interface, the materials may be those commonly used for joint
replacements including but not limited to: (1) Titanium Alloys such
as Ti6Al4V; (2) Chrome Cobalt Molybdenum Alloys; and (3) Stainless
Steel. The joint replacement may also include a bioactive
agent.
The invention may be used for biologic regeneration of an
intervertebral disc. Current attempts to resume partial or even
full disc functions include disc regeneration by applying the
state-of-art tissue engineering strategies. One key principle to
conduct such strategies is to generate two distinct anatomic
regions on the designed scaffolds that make up the intervertebral
disc (IVD) and culture corresponding parenchymal cells at the
central region resembling nucleus pulposus (NP) and the peripheral
region for annulus fibrosus (AF). However, the concept has been
only tested subcutaneously in a few studies. If the approach would
be applied in situ, one can imagine there will be inevitably
critical hurdles that can hinder any successfulness of full
functional disc regeneration. The major concern of engineering full
functional disc is cell survival. It is known that disc tissue is
avascular with very low cellular density only 1% to 2% of the
tissue volume. IVD cells, especially NP cells, rely highly on the
nutrient supply diffused through the cartilaginous endplates on the
superior and inferior surfaces. When a discectomy is executed, the
endplates are exposed, and the insertion of the scaffold may
interfere with the endplates due to the non-physical contact. In
addition, the interface between the scaffold and the endplates may
not be able to become fully integrated during neo-disc tissue
formation. The situation will endanger the implanted cells by
starving them away from the diffused nutrition and may result in
significant cell death and fail the full disc regeneration.
As the alternative, the present invention proposes unified fibrous
tissue regeneration for disc replacement. Originated from the
clinical investigation, it is well known that some cases of
interbody fusion can develop into asymptomatic pseudarthrosis,
which indicates a non-solid, fibrous union rather than solid bone
fusion. The reason physicians tend to explain for this phenomenon
is that it may be because sufficient amount of fibrous tissue
formation occurs intervertebrally and it provides sufficient
stiffness to maintain the disc height, while preserving certain
amount of motion without disturbing nerve roots. Moreover, it is
speculated that with the formation of fibrous union, contact stress
from body weight becomes more evenly distributed on the new fibrous
construct, which, very possibly, reduces the etiology of axial
discogenic pain.
By applying the approach already described on engineering
scaffolds, the present invention can design a scaffold with the
same inherent disc tissue properties to provide immediate support
post-operatively. As it has been proven that sclerosing agents
induce scarring for fibrosis and tissue contraction, the present
invention combines these agents to increase fibrous tissue union in
a controlled manner to confine the new fibrous tissue within the
designed architecture. Any therapeutic proteins, growth factors,
progenitor cells, and molecules/compounds, if aiming at
beneficiating fibrous tissue formation, can be also included in our
designed scaffold. Vehicles in gel forms or microspheres may also
be associated with the usage of this invention as substantial
components for applying the proposed unified fibrous tissue
regeneration for disc replacement.
Once the intervertebral scaffolding image-design dataset is
created, it can be automatically converted into a surface
representation in .stl file format (stereolithography triangular
facet data). This makes it possible to fabricate the intervertebral
scaffolding from any type of Solid Free-Form Fabrication (SFF)
system using either direct or indirect methods. The direct SFF
methods include, but are not limited to: (1) Selective Laser
Sintering (SLS); (2) Stereolithography (SLA); (3) Fused Deposition
Modeling (FDM); and (4) Selective Laser Melting (SLM). One example
solid freeform fabrication method may be found in U.S. Patent
Application Publication No. 2003/0074096, which is incorporated
herein by reference as if fully set forth herein.
Indirect methods are based on casting biomaterials, such as those
listed above, into a mold created on a SFF system. In addition to
the above SFF systems, the molds may also be created on direct 3D
printing systems, including those systems that print wax. The
indirect methods described in U.S. Patent Application Publication
No. 2003/0006534 and U.S. Pat. No. 7,087,200 (which are both
incorporated herein by reference as if fully set forth herein) may
be used to make the disc scaffold.
The methodology of the invention has been implemented to make
scaffolds for temporomandibular joint repair in a Yucatan Minipig
model. The design procedure involved taking a CT scan of the
minipig, using image-based techniques to design and fabricate the
scaffold, and surgically implanting the scaffold. FIG. 10 shows the
steps of an example procedure for mandibular condyle engineering
from image to fabricated scaffold. Note that this scaffold has
features created uniquely from image-based design, including a
wrap-around ramus collar that allows surgical fixation, as shown
with the screw holes.
Referring to FIG. 10, a spherical void architecture design 102 is
chosen for the cartilage (surface) region of the image based
design. An orthogonal strut architecture design 104 is chosen for
the bone region of the image based design. The microstructure
designs 102, 104 may be created using the image based design
methods described in U.S. Patent Application Publication No.
2003/0069718. The resulting CT scan images provide the condyle
shell anatomic external shape and design space for the scaffold
110. These images are stored as density distribution within a voxel
dataset. The method merges the anatomic and architecture databases
(see arrows 112, 113, 114). The method converts the voxel design to
a surface or wire frame geometry (see arrow 115). The method
fabricates the design scaffold from biomaterial using direct or
indirect (casting) solid free form techniques (see arrow 116).
In addition, working prototypes have been built of a cervical disc
design with anterior fixation plate and designed microstructure.
See FIG. 11. The scaffold 120 of FIG. 11 includes the wavy fibered
microstructure 32 in the correct anatomic shape for a natural
intervertebral disc. A top fixation plate 125 includes spaced apart
fastener holes 146a, (second hole not shown), and a top central
U-shaped cutaway section 147. A bottom fixation plate 151 includes
spaced apart fastener holes 152a, 152b, and a bottom central
inverted U-shaped cutaway section 153. The wavy fibered
microstructure 32 is integral with the fixation plates 125, 151.
When used in intervertebral disc repair, the wavy fibered
microstructure 32 of the scaffold 120 would be positioned in the
intervertebral space created by removal of the intervertebral disc
between adjacent vertebrae. Fasteners would be inserted in fastener
holes 146a, (second hole not shown), for anterior attachment to a
first upper vertebra, and fasteners would be inserted in fastener
holes 152a, 152b for anterior attachment to an adjacent second
lower vertebra. The top end surface 154 of the wavy fibered
microstructure 32 would contact a lower surface of the first upper
vertebra, and the opposite bottom end surface 155 of the wavy
fibered microstructure 32 would contact an upper surface of the
second lower vertebra. The wavy fibered microstructure 32 thereby
provides mechanical load bearing support between the first upper
vertebra and the second lower vertebra. The plates 125, 151 may
include throughholes to allow fluid into the interior spaces of the
scaffold to minimize any problems associated with tissue blockage
of fluid. Optionally, flaps (not shown) can be provided on the
plates 125, 151 to prevent backing out of the fasteners (e.g.,
fixation screws). In one embodiment, the fixation screws can be
formed using the same biocompatible and biodegradable material with
an osteoconductive mineral coating, and a bioactive agent
associated with the biodegradable material and/or the coating.
The scaffold 120 can comprise a porous biocompatible and
biodegradable (if desired) porous material selected from polymeric
materials, metallic materials, ceramic materials and mixtures
thereof. In one example embodiment, the scaffold 120 is formed from
polycaprolactone, a biocompatible and biodegradable polymer.
However, other polymers such as polylactide, polyglycolide,
poly(lactide-glycolide), poly(propylene fumarate),
poly(caprolactone fumarate), polyethylene glycol, and
poly(glycolide-co-caprolactone) may be advantageous for forming the
scaffold 120.
The vertical dimensions of the wavy fibered microstructure 32 in
FIG. 11 can be adjusted accordingly for various different
intervertebral distances. Likewise, the horizontal length of the
fixation plates 125, 151 and their spatial relationship can be
varied to ensure proper location of the fastener holes 146a,
(second hole not shown), 152a, 152b adjacent the first upper
vertebra and the second lower vertebra for securing the scaffold
120 to the first upper vertebra and the second lower vertebra. By
varying the dimensions of the wavy fibered microstructure 32 and
the fixation plates 125, 151 different size scaffolds 120 can be
provided for selection by a surgeon.
This disc scaffold 120 also has features created uniquely from
image-based design, including plates 125, 151 that allow surgical
fixation, as shown with the fastener holes. Various regions of the
disc scaffold 120 can include the mineral coatings and associated
bioactive agent. For example, top and bottom end regions that are
positioned near the opposed vertebrae can be coated with continuous
or islands of the coating and associated bioactive agent so that
bone growth is induced, while interior sections of the disc may not
include coatings and associated bioactive agent in order to promote
growth of fibrous tissue.
Because placement of the disc scaffold 120 of FIG. 11 may be
performed using a medical imaging device and techniques (e.g.,
fluoroscopic observation), the disc scaffold 120 may further
include at least one marking including a tracer that provides
enhanced visibility via the medical imaging device. For example,
non-limiting examples of radiopaque materials for enhanced
visibility during fluoroscopy include barium sulfate, tungsten,
tantalum, zirconium, platinum, gold, silver, stainless steel,
titanium, alloys thereof, and mixtures thereof. Radiopaque markings
can be used as an alignment aid in verifying the proper positioning
of the disc scaffold. Also, the scaffold 120 may include a region
of no material or radiolucent material such that the region forms
an imaging window for enhanced visibility through the imaging
window via a medical imaging device.
Therefore, it can be seen that the invention provides a method of
designing an intervertebral body scaffolding with controlled
elastic and permeability properties that may mimic that natural
function of vertebral discs. The designed permeability will allow
nutrients to diffuse into the disc to allow survival of delivered
cells or cells that migrate into the disc. Disc scaffolding
permeability could also be designed to mimic the permeability
distribution of normal discs. In addition, with the wavy fibered
microstructure, the disc scaffold could exhibit nonlinear behavior
similar to human intervertebral disc. This capability is not seen
in prior artificial discs, tissue engineered discs, or spine fusion
approaches. Furthermore, the disc may be fabricated as a composite
material.
The invention also provides a method of designing an osteochondral
scaffold design with a joint interface design. The invention
includes the ability to design effective mechanical and mass
transport properties of the interface and the ability to fabricate
these controlled microstructures. In addition, invention includes
the ability to readily fabricate adjunct surgical fixation based on
anatomic features.
The invention also provides a method of designing a joint
replacement. The invention provides methods and devices that
stabilize a joint, promote fibrous tissue union of adjacent bones,
and allow for motion between adjacent bones.
Although the invention has been described in considerable detail
with reference to certain embodiments, one skilled in the art will
appreciate that the present invention can be practiced by other
than the described embodiments, which have been presented for
purposes of illustration and not of limitation. In particular, the
methods and devices described herein can used to promote fibrous
union between any bone surfaces. Therefore, the scope of the
appended claims should not be limited to the description of the
embodiments contained herein.
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